The present invention relates to a method for repairing cracks in a trailing edge portion of a turbine blade.
Axial cracks initiating at the root trailing edge cooling hole occur on turbine blades used in industrial applications. The cracks are caused by thermal mechanical fatigue. Typically, the cracks initiate from both the concave and the convex side of the root trailing edge cooling hole and run axially towards the leading edge of the blade. Since the turbine blades are otherwise serviceable, a method for effectively repairing these cracks is needed.
Accordingly, it is an object of the present invention to provide a method for repairing cracks in a trailing edge portion of a turbine blade.
It is a further object of the present invention to provide a repair method as above which has particular utility in the repair of cracks initiating at a root trailing edge cooling hole.
It is yet a further object of the present invention to provide a method as above which increases the service life of the repaired turbine blade.
The foregoing objects are attained by the method of the present invention.
In accordance with the present invention, a method for repairing a turbine blade having a crack in a trailing edge portion of the turbine blade is provided. The method broadly comprises cutting back the trailing edge portion of the concave and convex surfaces adjoining the trailing edge portion to a depth greater than the length of the crack. Concurrent with the cut back procedure, the portion of the turbine blade between the platform and the cut back trailing edge portion is shaped using a compound radius to eliminate the presence of any cusp on the trailing edge. Further, those edges remaining after the cut back procedure are blended to a smooth radius to minimize stress concentration and aerodynamic losses. The cut back trailing edge portion is also faired into the original trailing edge profile, preferably at the approximate mid-span, to minimize aerodynamic impact.
In accordance with the present invention, a thermal barrier coat is applied to the repaired turbine blade to increase its service life. Prior to the application of the thermal barrier coating, the tip length of the turbine blade is modified to account for reduced substrate temperature of the repaired turbine blade.
Other details of the repair method of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.